xtables: move icmp/icmpv6 logic to xt_tcpudp

icmp/icmp6 matches are baked into ip(6)_tables.ko.

This means that even if iptables-nft is used, a rule like
"-p icmp --icmp-type 1" will load the ip(6)tables modules.

Move them to xt_tcpdudp.ko instead to avoid this.

This will also allow to eventually add kconfig knobs to build kernels
that support iptables-nft but not iptables-legacy (old set/getsockopt
interface).

Signed-off-by: Florian Westphal <fw@strlen.de>